package main

// The first breadcrumbs, written before anything else can fail.
//
// OpsLog keeps its log in the data folder, which lives beside the executable —
// so every fault that happens BEFORE that folder exists is invisible. Reported
// from a Windows 10 machine: "the process appears, no data folder is created,
// nothing starts", with no file anywhere to say why. There was nothing to read
// because the only place we write to had not been created yet.
//
// This writes to %LOCALAPPDATA%\OpsLog\startup.log instead: a folder Windows
// guarantees is writable for the user, whatever OpsLog itself was installed
// into. It records the handful of milestones between the process starting and
// the window appearing, and nothing else — it is not a second log, it is the
// answer to "it does not start".

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// bootLogPath is the file, or "" when even LOCALAPPDATA is unavailable.
func bootLogPath() string {
	dir := os.Getenv("LOCALAPPDATA")
	if strings.TrimSpace(dir) == "" {
		dir = os.TempDir()
	}
	if dir == "" {
		return ""
	}
	dir = filepath.Join(dir, "OpsLog")
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return ""
	}
	return filepath.Join(dir, "startup.log")
}

// bootLog appends one line. Never fails loudly: it exists to explain a failure,
// so it must not become one.
func bootLog(format string, args ...any) {
	p := bootLogPath()
	if p == "" {
		return
	}
	f, err := os.OpenFile(p, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o644)
	if err != nil {
		return
	}
	defer f.Close()
	// Trimmed when it gets long. A startup log that grows for two years is a
	// file nobody opens, and the interesting launch is always the last one.
	if fi, err := f.Stat(); err == nil && fi.Size() > 256*1024 {
		f.Close()
		_ = os.Remove(p)
		f, err = os.OpenFile(p, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o644)
		if err != nil {
			return
		}
		defer f.Close()
	}
	fmt.Fprintf(f, "%s %s\n", time.Now().Format("2006-01-02 15:04:05.000"), fmt.Sprintf(format, args...))
}

// bootLogLaunch records what was launched and from where.
func bootLogLaunch() {
	exe, _ := os.Executable()
	bootLog("launch: %s %v", exe, os.Args[1:])
}

// checkDataDirWritable makes sure the folder OpsLog keeps everything in can
// actually be created and written to, and says exactly what failed if not.
//
// The data folder sits beside the executable, which is fine on a stick or in a
// home directory and refused outright under Program Files — where Windows
// silently denies the write to anything not elevated. That refusal used to end
// the launch with no window and no message.
func checkDataDirWritable() error {
	dir, err := userDataDir()
	if err != nil {
		return fmt.Errorf("cannot work out where to keep the data: %w", err)
	}
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return fmt.Errorf("cannot create the data folder %s: %w", dir, err)
	}
	probe := filepath.Join(dir, ".writetest")
	if err := os.WriteFile(probe, []byte("ok"), 0o644); err != nil {
		return fmt.Errorf("the data folder %s cannot be written to: %w", dir, err)
	}
	_ = os.Remove(probe)
	bootLog("data dir ok: %s", dir)
	return nil
}